Where does the waste material in the body come from and why does the body need to get rid of these waste materials? Why does food need to be digested?

Answer the use of flood plains and irrigation;

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.

It would be tomatoes i believe